scholarly journals Models for moisture estimation in different horizons of yellow argisol using TDR

2017 ◽  
Vol 38 (4) ◽  
pp. 1727
Author(s):  
Karla Silva Santos Alvares de Almeida ◽  
Luciano Da Silva Souza ◽  
Vital Pedro Da Silva Paz ◽  
Maurício Antônio Coelho Filho ◽  
Eduardo Holzapfel Hoces
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Advantages And Disadvantages ◽  
Disturbed Soil ◽  
Cubic Polynomial ◽  
Indirect Technique ◽  
Moisture Estimation

The determination of soil moisture is very important because it is the property with the most influence on the dielectric constant of the medium. Time-domain reflectometry (TDR) is an indirect technique used to estimate the water content of the soil (?) based on its dielectric constant (Ka). Like any other technique, it has advantages and disadvantages. Among the major disadvantages is the need for calibration, which requires consideration of the soil characteristics. This study aimed to perform the calibration of a TDR100 device to estimate the volumetric water content of four horizons of a Yellow Argisol. Calibration was performed under laboratory conditions using disturbed soil samples contained in PVC columns. The three rods of the handcrafted probes were vertically installed in the soil columns. Weight measurements with digital scales and daily readings of the dielectric constant with the TDR device were taken. For all soil horizons evaluated, the best fits between the dielectric constant and the volumetric water content were related to the cubic polynomial model. The Ledieu model overestimated by approximately 68 % the volumetric water content in the A and AB horizons, and underestimating by 69 % in Bt2, in relation to volumetric water content obtained by gravimetry. The underestimation by linear, Topp, Roth, and Malicki models ranged from 50 % to 85 % for all horizons.

scholarly journals Construction and calibration of TDR probes for volumetric water content estimation in a Distroferric Red Latosol

2013 ◽  
Vol 33 (5) ◽  
pp. 919-928 ◽  
Author(s):  
Rosimaldo Soncela ◽  
Silvio C. Sampaio ◽  
Marcio A. Vilas Boas ◽  
Maria H. F. Tavares ◽  
Adriana Smanhotto
Keyword(s):  
Water Content ◽  
Irrigation Management ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Coefficient Of Determination ◽  
Calibration Model ◽  
Advantages And Disadvantages ◽  
Disturbed Soil ◽  
Red Latosol ◽  
The Time Domain

The determination of volumetric water content of soils is an important factor in irrigation management. Among the indirect methods for estimating, the time-domain reflectometry (TDR) technique has received a significant attention. Like any other technique, it has advantages and disadvantages, but its greatest disadvantage is the need of calibration and high cost of acquisition. The main goal of this study was to establish a calibration model for the TDR equipment, Trase System Model 6050X1, to estimate the volumetric water content in a Distroferric Red Latosol. The calibration was carried out in a laboratory with disturbed soil samples under study, packed in PVC columns of a volume of 0.0078m³. The TDR probes were handcrafted with three rods and 0.20m long. They were vertically installed in soil columns, with a total of five probes per column and sixteen columns. The weightings were carried out in a digital scale, while daily readings of dielectric constant were obtained in TDR equipment. The linear model θν = 0.0103 Ka + 0.1900 to estimate the studied volumetric water content showed an excellent coefficient of determination (0.93), enabling the use of probes in indirect estimation of soil moisture.

scholarly journals Time domain reflectrometry measurements using a movable obstacle for the determination of dielectric profiles

2008 ◽  
Vol 6 ◽  
pp. 1-4
Author(s):  
B. Will ◽  
M. Gerding ◽  
S. Schultz ◽  
B. Schiek
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Time Domain ◽  
Measurement Techniques ◽  
Measurement Data ◽  
Time Domain Reflectometry ◽  
Dielectric Measurement ◽  
Effective Dielectric Constant ◽  
Pulse Delay

Abstract. Microwave techniques for the measurement of the permittivity of soils including the water content of soils and other materials, especially TDR (time domain reflectometry), have become accepted as routine measurement techniques. This summary deals with an advanced use of the TDR principle for the determination of the water content of soil along a probe. The basis of the advanced TDR technique is a waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which the water content is estimated, and an obstacle, which can mechanically be moved along the probe and which acts as a reference reflection for the TDR system with an exactly known position. Based on the known mechanical position of the reference reflection, the measured electrical position can be used as a measure for the effective dielectric constant of the environment. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement. A conventional industrial TDR-system, operating in the baseband, is used for the signal generation and for the evaluation of the pulse delay time of the obstacle reflection. Thus, a cost effective method for the acquisition of the dielectric measurement data is available.

scholarly journals Experimental Determination of TDR Calibration Relationship for Pyroclastic Ashes of Campania (Italy)

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3727 ◽  
Author(s):  
Giovanna Capparelli ◽  
Gennaro Spolverino ◽  
Roberto Greco
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Organic Matter Content ◽  
Free Water ◽  
Time Domain Reflectometry ◽  
Dielectric Constants ◽  
Phase System ◽  
Three Phase ◽  
The Relationship

Time domain reflectometry (TDR) is one of the most widely used techniques for indirect determination of soil volumetric water content (θ). TDR measures the relative dielectric constant (εr) which, in a three-phase system like the soil, depends on water, air, and solid matrix dielectric constants. Since dielectric constant of water is much larger than the other two, εr of bulk soil mainly depends on water content. In many cases, the application of TDR requires a specific calibration of the relationship θ(εr) to get quantitatively accurate estimates of soil water content. In fact, the relationship θ(εr) is influenced by various soil properties, such as clay content, organic matter content, bulk density, and aggregation. Numerous studies have shown that pyroclastic soils often exhibit a peculiar dielectric behavior. In Campania (Southern Italy) wide mountainous areas are covered by layered pyroclastic deposits of ashes (loamy sands) and pumices (sandy gravels), often involved in the triggering of landslides induced by rainwater infiltration. Reliable field measurements of water content of such soils are therefore important for the assessment of landslide risk. Hence, in this paper, the θ(εr) relationship has been experimentally determined on samples of typical pyroclastic soil of Campania, collected around Sarno, reconstituted with different porosities. The aim of the study is to identify specific calibration relationships for such soils based not only on empirical approaches. In this respect, a three-phase dielectric mixing model with a variable exponent is introduced, and the variable value of the exponent is related to the different dielectric properties of bond and free water within the soil pores.

Determining Moisture Content of Soil Layers with Time Domain Reflectometry and Micromechanics

2008 ◽  
Vol 2053 (1) ◽  
pp. 30-38 ◽  
Author(s):  
Sang Ick Lee ◽  
Dan G. Zollinger ◽  
Robert L. Lytton
Keyword(s):  
Dielectric Constant ◽  
Soil Moisture ◽  
Moisture Content ◽  
Water Content ◽  
Time Domain ◽  
Soil Moisture Content ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Dry Density

Although the moisture condition of pavement sublayers can significantly affect pavement performance, accurate interpretation of in situ soil moisture measurements has been difficult to achieve because of the limitations of existing methods. Time domain reflectometry (TDR), originally developed to detect breaks or shorts in electrical conductors, has been used for measuring parameters related to the in situ soil moisture content. However, the apparent length method currently used to determine dielectric constant ignores other electrical properties of the conducting medium that may affect the interpretation of TDR trace to determine soil moisture. Furthermore, the existing methods for computing volumetric water content ignore the variations of dry density and determine the model parameters with assumption or regression analysis. These deficiencies can, in many cases, create a significant systematic error in the final determination of volumetric water content. To minimize these errors and improve the accuracy of moisture content estimate, a new three-step approach was proposed. The approach uses the transmission line equation to calculate the dielectric constant, conductivity, and reflectivity of a soil mixture. A micromechanics and self-consistent scheme was used to determine the volumetric moisture content and dry density on the basis of calibrated values of the solid and water dielectric constants. The system identification method was used iteratively to solve for dielectric parameters, soil moisture content, and dry density values. The validation of the new approach with ground-truth data indicated that the calculated errors were significantly less than those of existing method.

scholarly journals Application of time domain reflectometry to determination of volumetric water content in rock

1998 ◽  
Vol 34 (10) ◽  
pp. 2623-2631 ◽  
Author(s):  
Toshihiro Sakaki ◽  
Kozo Sugihara ◽  
Tetsuya Adachi ◽  
Kaoru Nishida ◽  
Wei-ren Lin
Keyword(s):  
Water Content ◽  
Time Domain ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content

scholarly journals Determination of the permittivity of soils by use of double transmission measurements

2009 ◽  
Vol 7 ◽  
pp. 1-4 ◽  
Author(s):  
B. Will ◽  
M. Gerding
Keyword(s):  
Dielectric Constant ◽  
Water Content ◽  
Delay Time ◽  
Effective Permittivity ◽  
Time Domain Reflectometry ◽  
Effective Dielectric Constant ◽  
Step Size ◽  
Transmission Method ◽  
Average Value

Abstract. Delay time measurements, e.g. time domain reflectometry (TDR), are a well-established method for the measurement of permittivity of various materials, especially soils. However, common measurement systems only provide one average value of the dielectric constant along the length of the TDR probe. This contribution deals with an advanced application of the TDR principle, the so-called double transmission method, for the determination of the water content of soil along a probe. To apply the advanced TDR technique, a probe, realized by a combination of a transmission line and a dielectric obstacle, which can mechanically be moved along the probe, is used. The probe is inserted into the soil to measure the effective soil permittivity. Thus, the water content along the probe can be estimated by means of the effective permittivity. Based on the known mechanical position of the reflection at the end of the probe and the position of the obstacle, the measured delay time can be used as a measure for the effective dielectric constant of the environment surrounding the obstacle. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement.

Using time domain reflectometry in triaxial testing

2000 ◽  
Vol 37 (6) ◽  
pp. 1325-1331
Author(s):  
J LH Grozic ◽  
M E Lefebvre ◽  
P K Robertson ◽  
N R Morgenstern
Keyword(s):  
Cyclic Loading ◽  
Water Content ◽  
Time Domain ◽  
Void Ratio ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Degree Of Saturation ◽  
Triaxial Testing ◽  
Empirical Correlations ◽  
Static And Cyclic Loading

Time domain reflectometry (TDR) can be used to determine the volumetric water content of soils. This note describes the utilization of a TDR miniprobe in triaxial testing. The TDR performance was examined with a series of tests that not only proved its reliability but also resulted in two empirical correlations. Using these correlations, the degree of saturation and volumetric water content during triaxial testing could be determined. The TDR was then put to use in a laboratory program designed to investigate the response of loose gassy sand under static and cyclic loading. Because of the TDR measurements it was possible to determine the degree of saturation and void ratio of the gassy specimens. The TDR miniprobe proved to be accurate, simple to use, and inexpensive to build.Key words: time domain reflectometry, TDR, triaxial testing, gassy, unsaturated.

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